Draw circles and arcs, cut pieces away, and see the area & perimeter equations build themselves.
Click-drag to draw (◯ circles or ╱ lines) · drag shapes to move, the ◆ rim handle to resize · lines through circles label themselves as chords, diameters, or tangents · make Pie or Segment cuts in the inspector · centres and edges snap
Draw or select a shape to change its radius, turn it into a semicircle or arc, or make it a cut-out.